In snow skiing, turns are initiated and sustained by applying pressure to the longitudinal edges of both skis. It is generally understood that turning is much easier if the skier has a slightly "knock-kneed" posture, with the skier's lower legs between about one and two degrees inside vertical when the skis are horizontal. In this position, somewhat more than half of the skier's weight is placed on the inside edges of the skis.
In general, the rigid state-of-the-art ski boots, and the ski bindings by which the boots are releasably secured to the skis, fix the angle of the skier's lower legs in the plane transverse to the direction of elongation of the skis with respect to the upper suface of the skis (hereinafter, the "cant angle"). The cant angle obtained varies substantially with respect to the inherent physiognomy of the individual skier and the design of the particular ski boot.
It is known that adjustment of the cant angle to obtain the preferred "inside-edge" weight distribution is desirable in order to provide optimum control and consequently skill and enjoyment. As noted, the optimal cant angle is only concidentally obtained when a skier selects a new pair of boots; accordingly, the art recognizes that the fit of ski boots with respect to the skis is preferably customized in order to obtain the ideal cant angle.
A number of methods exist for adjusting the the cant angle between the upper surface of the ski and the skier's lower leg. These include the placement of wedge-shaped or spaced asymmetrical shims under the ski bindings, employment of interchangeable boot soles providing various cant angles between the boots and ski bindings, modification of the boots, and adjustable cuffs incorporated into certain boot designs. However, unless the cant angle itself can be precisely determined, one must follow a time-consuming tedious trial and error approach to boot fitting using any of these techniques.
In the past, shimming requirements have been crudely estimated by dropping a plumb line from a vertical mark formed on the skier's knee to the front edge of the boot, followed by repetitively varying the thickness of shims placed between the boot and ski until the plumb line came within a prescribed distance from the boot centerline.
An apparatus for indicating the cant angle provided to a given skier wearing a particular pair of boots is disclosed in U.S. Pat. No. 3,726,015 to Neumann. The Neumann apparatus comprises an elongate flat base plate supported to allow tilting about the longitudinal axis and having a wand extending upward from the forward end of the base plate, perpendicular to the longitudinal axis. The wand is also pivoted about an axis perpendicular to the direction of elongation of the ski, allowing the skier to assume various degrees of knee bend. A knee clamp comprising opposed knee-engaging plates simultaneously drawn toward one another by rotation of a lead screw having oppositely-threaded portions may be provided to ensure centering of the wand on the skier's knee.
In use of the Neumann apparatus, the skier stands in skiing posture on the plate with the toe of the boot centered against the base of the wand. The misalignment between the skier's lower leg and the wand approximates the cant angle between the boot sole plane and the lower leg. Correction is then to be made on a trial-and-error basis, either by modifying the boot itself, or by adding various shims, until alignment of the wand and knee indicates that the desired alignment has been achieved. That is, Neumann provides no scale or other instrument whereby the amount of the appropriate correction to be made can be determined directly; accordingly, use of the Neumann device, involving repetitive steps of the skier's putting on the boot, having a measurement made, removing the boot, modifying the boot or shims, and repeating these steps, would be rather time-consuming and awkward.
Furthermore, while Neumann's provision of the knee clamp having opposed, cooperatively-moved knee-engaging plates does provide a degree of accuracy in locating the center of the knee, as this clamp is fixed to the wand the skier will tend to distort his or her natural posture in order to fit the knee into the clamp.
An instrument providing a direct measurement of the skier's "natural" cant angle would be much more useful in provision of the appropriate correction. In a field where the skier's performance and enjoyment of the sport is directly impacted by variations in cant angle of as little as one-half degree, the imprecision of this and other prior art approaches to cant angle measurement and correction fails to meet the needs of modern competitive and recreational skiers.